The present invention relates to a conductive pattern incorporated in a multilayered substrate such as a multilayered LC component, which conductive pattern has low electric resistivity, is superior in adhesion to the substrate, does not cause substrate cracking during plating and does not increase dielectric loss, a multilayered substrate incorporating such a conductive pattern, and a method of fabricating a multilayered substrate.
In recent years, the miniaturization of electronic devices has made it necessary to miniaturize the electrical components incorporated in these devices. In the particular case of components that utilize ceramics and circuit substrates, such as inductors, capacitors and filters, miniaturization is achieved by laminating them into a multilayered structure. Such a multilayered component is fabricated by printing a conductive paste on green sheets fabricated by a sheet method, printing method or the like to apply a mixture of ceramic powder and organic binder, thereafter laminating, crimping, cutting and sintering the sheets, and then forming external electrodes on the laminated body. In general, the conductive paste is composed of metal powder dispersed in an organic binder and an organic solvent.
Ag (silver), which has low resistivity, is used as the conductive material to obtain a low-resistivity conductive paste for use in LC components requiring a high quality factor (Q value), filter components, and circuit substrates. The sintering temperature of the ceramic material, which is a material of the substrate sintered together with the conductive material, must be lower than the melting point of Ag (960.5xc2x0 C.). A glass-ceramic, i.e., a ceramic containing a glass material that works as a sintering assistant, is commonly used as the ceramic material.
However, the contraction starting temperature of Ag is as low as 300xc2x0 C.-500xc2x0 C., while the contraction starting temperature of a glass-ceramic is 700xc2x0 C.-940xc2x0 C. Therefore, when Ag is used as the conductive material of the conductive paste, stress arises between the conductive layer and the ceramic layer because the contractions are not of the same degree. As a result, defects such as cracks, delaminations, and the like may be induced. Thus, the sintering characteristics of the Ag powder and the ceramic material included in the conductive paste should be identical. Specifically, the degrees of contraction of the ceramic material and the conductive material should be identical at every temperature during sintering. Thus, some method is needed for restraining the progress of the Ag sintering. One known method for restraining the progress of the Ag sintering is to add glass powder made of the SiO2xe2x80x94Al2O3 family or the like to the conductive paste. According to this method, cracking is prevented because the progress of the Ag sintering is restrained by the glass powder. Japanese Patent Laid Open No. 6-20516, for example, teaches another method in which Cr or Cr compound, serving as sintering controller, and Al2O3, PdO or any of various other ceramics, serving as inorganic binder, are added to the conductive composition in order to prevent the substrate from experiencing appearance defects such as warping and cracks, and to enhance the adhesive strength to the substrate.
However, in order to thoroughly avoid warping or cracks, it is necessary to add a large amount of glass. When such a conductive composition is used for the internal conductors incorporated in a multilayered substrate having capacitors (capacitor integrated), various problems arise, including increased conductor resistance and increased dielectric loss. Moreover, experiments conducted by the inventors revealed that use of a conductive composition with Cr or Cr compound added for the electrodes of the capacitors increases dielectric loss.
The objects of the present invention are therefore to provide a conductive pattern incorporated in a multilayered substrate such as a multilayered LC component, which conductive pattern has low electric resistivity, is superior in adhesion to a substrate, does not cause substrate cracking during plating and does not increase dielectric loss, to provide a multilayered substrate incorporating such a conductive pattern, and to provide a method of fabricating a multilayered substrate.
Through extensive research for realizing a multilayered ceramic component that does not crack or warp and experiences no degradation of electrical characteristics, the inventors of the present invention found that addition of Cr to the conductive composition increases dielectric loss because the Cr diffuses into the substrate and reacts with the glass component of the substrate so that a glass having high dielectric loss is formed. Their research further led to the discovery that adding Mn to the conductive composition effectively prevents Cr from diffusing in excess.
Based on these technical concepts, the above objects of the present invention can be accomplished as set out in the following:
The above and other objects of the present invention can be accomplished by a conductive pattern incorporated in a multilayered substrate characterized in that the conductive pattern includes Ag as a main component, Cr and/or Cr compound, and Mn and/or Mn compound.
According to this aspect of the present invention, the conductive pattern has low electric resistivity, is superior in adhesion to a substrate and does not cause substrate cracking during plating because Cr and/or Cr compound are added to Ag as a main component of the conductive pattern, while increase of dielectric loss is prevented because Mn and/or Mn compound is added.
In a preferred aspect of the present invention, Cr and/or Cr compound content calculated based on Cr2O3 is 0.1-2.0 mass % relative to Ag.
In a further preferred aspect of the present invention, Mn and/or Mn compound content calculated based on MnO2 is 0.1-5.0 mass % relative to Ag.
In a further preferred aspect of the present invention, the conductive pattern further includes Al and/or Al compound.
In a further preferred aspect of the present invention, Al and/or Al compound content calculated based on Al2O3 is 0.1-1.0 mass % relative to Ag.
In a further preferred aspect of the present invention, the conductive pattern is a capacitor electrode.
The above and other objects of the present invention can be also accomplished by a multilayered substrate having a plurality of substrates and conductive patterns incorporated in the plurality of substrates characterized in that the conductive patterns include Ag as a main component, Cr and/or Cr compound, and Mn and/or Mn compound.
According to this aspect of the present invention, the conductive pattern has low electric resistivity, is superior in adhesion to the substrate and does not cause substrate cracking during plating because Cr and/or Cr compound are added to Ag as a main component of the conductive pattern, while increase of dielectric loss is prevented because Mn and/or Mn compound are added.
In a preferred aspect of the present invention, the substrates are made of a glass-ceramic material composed of a glass component and a ceramic component.
In a further preferred aspect of the present invention, the volume ratio between the glass component and ceramic component contents is 50:50 to 80:20.
In a further preferred aspect of the present invention, the glass component includes SiO2xe2x80x94ROxe2x80x94Al2O3xe2x80x94B2O3 (where R is alkaline earth metal).
In a further preferred aspect of the present invention, the ceramic component includes one or more components selected from the group consisting of Al2O3, TiO2, and TiO2 compound.
In a further preferred aspect of the present invention, the conductive pattern further includes Al and/or Al compound.
In a further preferred aspect of the present invention, the conductive patterns are capacitor electrodes.
The above and other objects of the present invention can be also accomplished by a method of fabricating a multilayered substrate comprising a step of preparing a conductive composition including metal powder containing Ag at not less than 95 mass %, a sintering restrainer containing Cr and/or Cr compound, a dielectric loss conditioner containing Mn and/or Mn compound, and a vehicle, a step of forming electrodes made of the conductive composition on a plurality of green sheets, a step of laminating the plurality of green sheets on which the electrodes are formed to form a laminated product, and a step of sintering the laminated product.
According to this aspect of the present invention, the conductive pattern has low electric resistivity, is superior in adhesion to the substrate, and does not cause substrate cracking during plating because Cr and/or Cr compound are added to Ag as a main component of the conductive pattern, while increase of dielectric loss is prevented because Mn and/or Mn compound are added.
In a preferred aspect of the present invention, Cr and/or Cr compound content calculated based on Cr2O3 is 0.1-2.0 mass % relative to the metal powder.
In a further preferred aspect of the present invention, Mn and/or Mn compound content calculated based on MnO2 is 0.1-5.0 mass % relative to the metal powder.
In a further preferred aspect of the present invention, the conductive composition further includes Al and/or Al compound.
In a further preferred aspect of the present invention, Al and/or Al compound calculated based on Al2O3 is 0.1-1.0 mass % relative to the metal powder.
In a further preferred aspect of the present invention, the metal powder has an average grain size of 0.1xcexcm-10 xcexcm.
In a further preferred aspect of the present invention, the sintering step is performed at a temperature of 750xc2x0 C.-940xc2x0 C.
Although Japanese Patent Laid Open No.5-41110 teaches a technique of adding a glass flit, Cr2O3, and MnO2 to a conductive paste including Ag powder and Pt powder, the technique is directed to a conductive paste used for a wiring pattern formed on the surface of a sintered multilayered substrate, not to a conductive paste incorporated in a multilayered substrate and sintered together with the substrate.